E85 Flex Fuel Specification

ASTM International developed a specification for gasoline-ethanol blends containing 51% to 83% ethanol to ensure proper vehicle starting, operation, and safety in varying temperature conditions. The table below shows the requirements of the ASTM D5798 Standard Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition Engines. Fuel retailers or fleets purchasing E85 should require their fuels to meet quality standards as a condition in their supply contracts in order to help guarantee their product is ASTM-compliant.

Like gasoline and diesel fuel, E85 and other ethanol-gasoline blends are adjusted seasonally and geographically to ensure proper starting and performance. For example, E85 sold during colder months often contains lower levels of ethanol to produce the vapor pressure necessary for starting in cold temperatures. For this reason, fueling site operators offering ethanol blends typically cannot carry over summer-blend E85 into the winter months. They must instead "blend down" any remaining summer fuel to meet the ASTM specification's requirements for winter temperature conditions. This can be done with relative ease by adding gasoline to the storage tank. On the other hand, there is no concern with carrying over winter fuel into the summer months because flexible-fuel vehicles can operate during warm weather on any blend of ethanol and gasoline. For retail stations, seasonal fuel adjustments are handled automatically at the wholesale fuel terminal.